Hammett spectral correlations in benzofuranyl flavonols

Available online at www.ilcpa.pl International Letters of Chemistry, Physics and Astronomy 6 (2014) 39-47 ISSN 2299-3843 Hammett spectral correlations in benzofuranyl flavonols G. Thirunarayanan1,*, K. G. Sekar2 1 Department of Chemistry, Annamalai University, Annamalainagar - 608002, Tamil Nadu, India 2 Department of Chemistry, National College, Tiruchirrappalli - 620001, Tamil Nadu, India *E-mail address: ABSTRACT A series containing eleven benzofuranyl flavonols have been prepared by cyclization of 3hydroxybenzofuranyl chalcones with 30 % hydrogen peroxide in the presence of sodium bicarbonate. The synthesized flavonols were characterized by their physical constants, analytical and spectroscopic data. The infrared spectral νOH, CO stretches(cm-1), NMR chemical shifts of OH, CO(δ, ppm) of these flavonols were assigned and correlated with Hammett substituent constants, F and R parameters using single and multi linear regression analysis. From the results of statistical analyses, the effects of substituents on the above group frequencies were discussed. Keywords: Benzofuranyl flavonols; Hammett equation; IR spectra; NMR spectra; Regression analysis 1. INTRODUCTION Hammett spectral correlation is useful for predicting the ground state equilibration of organic molecules such as unsaturated carbonyl compounds [1], alkenes [2], polyenes [3], acyl halides and its esters [4]. Infrared spectra are a good tool for analyzing the structure of organic molecules, qualitative and quantitative measurements, s-cis and s-trans equilibration of unsaturated ketones, anti- and gauche- form of acyl halides and esters [4,5]. The NMR spectroscopy was utilized for predicting spatial arrangements of the E or Z isomers and conformers in unsaturated ketones, pyrazolines and it derivatives [6,7]. The effect of substituents on the above molecular conformers and isomers also studied through Hammett substituent constants, F and R parameters [8]. Thirunarayanan have studied the effect of substituents on spectral frequencies in thiadiazole-2-amines [9]. Joseph et al have studied the effect of substituents on dimethyl phenyl chalcones by Hammett equation with spectral data [10]. Sekar and Thirunarayanan have studied the spectral correlation in pyrazoline derivatives [11]. The substituent effects on oxazine-2amines were studied using spectral data using single and multi-regression analysis [12]. Kamalakkannan et al have studied the substituent effects on 2-indolyl chalcones by electrochemical redox potential with Hammett equation [13]. International Letters of Chemistry, Physics and Astronomy 6 (2014) 39-47 Within the above view there is no report available for the study of effect of substituents on the 3-hydroxy-2-(substituted phenyl)-4H-pyrano[3,2-b][1]benzofuron-4-ones through spectral data using regression analysis. Therefore the authors have taken effort to prepare some 3-hydroxy-2-(substituted phenyl)-4H-pyrano[3,2-b][1]benzofuron-4-one derivatives and recorded the infrared and NMR spectra for studying the effect of substituents on the spectral frequencies. 2. EXPERIMENTAL 2. 1. General All chemicals and solvents used in this present study were procured from SigmaAldrich and Merck companies. The infrared spectra of all oxazine imines have been recorded in SHIMADUZ Fourier Transform IR spectrophotometer using KBr disc. The NMR spectra of all compounds were recorded in BRUKER AV 400 type spectrometer, using CDCl3 as a solvent, 400 MHz frequency was applied for recording 1H, 100 MHz for 13C NMR spectra, taking TMS as standard. 2. 2. General procedure for synthesis of 3-hydroxy-2-(substituted phenyl)-4H-pyrano [3, 2-b][1]benzofuron-4-one derivatives About 2 mmol of 3-hydroxybenzofuranyl chalcones, 5 mL of 5 % sodium bicarbonate, 10 mL of ethanol were vigorously stirred in the three necked flask under cooling condition (Scheme 1). To this reaction mixture, added drop-wise 5 mL 30 % hydrogen peroxide through dropping funnel for half an hour duration and continued the stirring to one hour and it was kept overnight. The mixture was diluted with 20 mL of water and acidified with concentrated H2SO4 (5-7 mL). The obtained solid product was filtered at the pump washed with water, dried and recrystallized with ethanol. The analytical, physical constants and spectroscopic data of synthesized substituted flavonols were presented in Table 1. Scheme 1. Synthesis of 3-hydroxy-2-(substituted phenyl)-4H-pyrano[3,2-b][1]benzofuron-4-ones. 40 International Letters of Chemistry, Physics and Astronomy 6 (2014) 39-47 3. RESULTS AND DISCUSSION In the present study, the author have investigated the effect of substituent on spectral frequencies of 3-hydroxy-2-(substituted phenyl)-4H-pyrano[3,2-b][1]benzofuron-4-ones using Hammett substituent constants, F and R parameters by linear regression analysis [1519]. Table 1. Analytical, physical constants and spectroscopic data of 3-hydroxy-2-(substituted phenyl)4H-pyrano[3,2-b][1]benzofuron-4-ones. Entry X M.F. M.W. m.p. (°C) Mass (m/z) IR (ν, cm-1) NMR (δ, ppm) OH CO OH CO 1 H C18H12O4 278 112-113 278[M+] 3410 1689 7.143 171.26 2 3-Br C18H11BrO4 341 138-139 341[M+], 343[M2+] 3414 1689 7.032 170.26 3 3-Cl C18H11ClO4 297 127-128 297[M+], 299[M2+] 3413 1690 7.101 170.32 4 4-Cl C18H11ClO4 297 144-145 (142-144) [14] 297[M+], 299[M2+] 3413 1690 7.132 170.03 5 4-NMe2 C20H17NO4 305 125-127 (123-129) [14] 305[M+] 3407 1688 7.093 171.68 6 2-OH C18H12O5 278 150-152 (153-156) [14] 278[M+] 3409 1686 7.349 171.61 7 4-OH C18H12O5 278 123-125 (122-124) [14] 278[M+] 3410 1691 7.214 171.24 8 4-OMe C19H14O5 292 145-146 (147-150) [14] 292[M+] 3403 1682 7.008 170.16 9 4-Me C19H14O4 276 123-124 (119-122) [14] 276[M+] 3406 1684 7.114 170.96 10 3-NO2 C18H11NO6 323 126-127 323[M+] 3415 1691 7.395 171.96 11 4-NO2 C18H11NO6 323 144-146 (143-145) [14] 323[M+] 3416 1693 7.413 173.76 41 International Letters of Chemistry, Physics and Astronomy 6 (2014) 39-47 Table 2. Results of statistical analysis of infrared ν(cm-1) OH, CO stretches, NMR chemical shifts of OH and CO (δ, ppm) of 3-hydroxy-2-(substituted phenyl)-4H-pyrano[3,2-b][1]benzofuron-4-ones with Hammett constants σ, σ+, σI, σR and F and R parameters. Frequency νOH νCO δOH Constants r I ρ s n σ 0.998 3410.02 7.372 2.28 11 σ+ 0.997 3411.18 4.223 2.63 11 σI 0.977 3406.39 13.103 2.69 11 σR 0.976 3412.65 9.870 3.39 11 F 0.967 3405.92 11.746 2.96 11 R 0.906 3412.77 7.081 3.31 11 σ 0.905 1688.16 4.123 2.77 9 σ+ 0.904 1688.77 2.101 2.99 9 σI 0.906 1685.88 8.119 2.74 10 σR 0.904 1689.76 6.118 2.99 9 F 0.905 1685.51 8.741 2.78 10 R 0.874 1689.62 3.704 3.12 11 σ 0.804 7.171 0.141 0.13 11 σ+ 0.884 7.192 0.077 0.13 11 σI 0.846 7.095 0.270 0.13 11 42 Correlated derivatives H, 3-Br, 3-Cl, 4-Cl, 4-NMe2, 2-OH, 4-OH, 4-OMe, 4-M (...truncated)